Highly radioactive liquid wastes are produced during isotope production processes. Even relatively dilute liquid radioactive wastes remain hazardous. Because of the large volume of aqueous waste produced, the handling, transportation and storage of such liquid radioactive waste remains problematic.
It would be desirable to convert solutions of hazardous material, such as radioactive liquids, into chemically stable, solid forms by evaporating solvent, removing adventitious or included solvent and thermally decomposing solute components within a vessel that, upon closure, is suitable for subsequent handling and storage. Volume reduction and waste immobilization are central to strategies for safely managing such hazards.
Solvent evaporation can, for example, be achieved in open vats, boilers, thin film evaporators, wiped film evaporators and rotary evaporators. However, such systems do not take a solution directly to a stable solid or chemical form. In such systems, the evaporation chamber is typically used repeatedly and is not adapted for subsequent processing and disposal. In addition, the cost and complexity of such fixed installations make them generally suitable only for processing relatively large volumes of waste solutions. Rotary calciners for large scale operations have been developed for similar applications but are not readily adapted to simple systems operating on a small scale. Calcination systems based on fluidized beds do not provide for containment of hazardous materials and require a separation process for recovery of the final product. Furnaces can be used for calcining materials inside refractory metal or ceramic containers, but are not readily modified to accommodate continuous feed of liquid wastes or to meet containment requirements for hazardous materials.
McGinnis, et al., “Development and Operation of a Unique Conversion/Solidification Process for Highly Radioactive and Fissile Uranium”, Nucl. Technol. 77, 210-219, (1987), describe a process in which waste solution is fed continuously into a heated vessel, but evaporation is from a bulk volume of liquid rather than a relatively small volume of solution distributed through a long channel.
U.S. Pat. No. 4,144,186 describes a process in which waste solution is denitrated, spray dried, and calcined prior to mixing with glass forming components to generate a solidified waste form.
There remains a need, therefore, for an apparatus and method for converting solutions of hazardous liquid materials, such as radioactive liquids, into chemically stable and solid forms; that is suitable for small scale operations; hot cell operations using remote-handling manipulators; rigorous containment of hazardous, fissile, or highly radioactive materials; and for combining evaporation, drying and thermal decomposition operations in a continuous process within a single vessel that is suitable for subsequent handling, storage, inspection and verification and disposal.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.